This invention relates generally to gas turbine engines and, more specifically, to a flowpath through a compressor rotor.
A gas turbine engine typically includes a multi-stage axial compressor with a number of compressor blade or airfoil rows extending radially outwardly from a common annular rim. The outer surface of the rotor rim typically defines the radially inner flowpath surface of the compressor as air is compressed from stage to stage. Centrifugal forces generated by the rotating blades are carried by portions of the rim directly below the blades. The centrifugal forces generate circumferential rim stress concentration between the rim and the blades.
Additionally, a thermal gradient between the annular rim and compressor bore during transient operations generates thermal stress which adversely impacts a low cycle fatigue (LCF) life of the rim. In addition, and in a blisk intergrally bladed disk configuration, the rim is exposed directly to the flowpath air, which increases the thermal gradient and the rim stress. Also, blade roots generate local forces which further increase rim stress.
The present invention, in one aspect, is a gas turbine engine rotor assembly including a rotor having a radially outer rim with an outer surface shaped to reduce rim stress between the outer rim and a blade and to direct air flow away from an interface between a blade and the rim, thus reducing aerodynamic performance losses. More particularly, and in an exemplary embodiment, the disk includes a radially inner hub, and a web extending between the hub and the rim, and a plurality of circumferentially spaced apart rotor blades extending radially outwardly from the rim. In the exemplary embodiment, the outer surface of the rim has a concave shape between adjacent blades with apexes located at interfaces between the blades and the rim.
The outer surface of the rotor rim defines the radially inner flowpath surface of the compressor as air is compressed from stage to stage. By providing that the rim outer surface has a concave shape between adjacent blades, rim stress between the blade and the rim is reduced. Additionally, the concave shape generally directs airflow away from immediately adjacent to the blade/rim interface and more towards a center of the flowpath between the adjacent blades. As a result, aerodynamic performance losses are reduced. Reducing such rim stress facilitates increasing the LCF life of the rim.